interface/wx/any.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        any.h
   3 // Purpose:     interface of wxAny
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9
  10 /**
  11     @class wxAny
  12
  13     The wxAny class represents a container for any type. Its value
  14     can be changed at run time, possibly to a different type of value.
  15
  16     wxAny is a backwards-incompatible (but convertible) successor class for
  17     wxVariant, essentially doing the same thing in a more modern, template-
  18     based manner and with transparent support for any user data type.
  19
  20     Some pseudo-code'ish example of use with arbitrary user data:
  21
  22     @code
  23     void SomeFunction()
  24     {
  25         MyClass myObject;
  26         wxAny any = myObject;
  27
  28         // Do something
  29         // ...
  30
  31         // Let's do a sanity check to make sure that any still holds
  32         // data of correct type.
  33         if ( any.CheckType<MyClass>() )
  34         {
  35             // Thank goodness, still a correct type.
  36             MyClass myObject2 = any.As<MyClass>();
  37         }
  38         else
  39         {
  40             // Something has gone horribly wrong!
  41             wxFAIL();
  42         }
  43     }
  44     @endcode
  45
  46     When compared to wxVariant, there are various internal implementation
  47     differences as well. For instance, wxAny only allocates separate data
  48     object in heap for large (ie. size in bytes more than
  49     WX_ANY_VALUE_BUFFER_SIZE) or 'non-movable' data types. Pointers, integers,
  50     bools etc. are fitted in the wxAny's own buffer without need for any extra
  51     allocation. Use following code to declare your own data type as 'movable':
  52
  53     @code
  54     #include "wx/meta/movable.h"
  55     WX_DECLARE_TYPE_MOVABLE(MyClass)
  56     @endcode
  57
  58     However, you must be aware that 'movable' means such data that can be
  59     copied with memcpy() without corrupting program integrity. For instance,
  60     movable objects usually cannot contain pointers or references to other
  61     data. wxRect, wxPoint, and wxSize are good examples of movable classes.
  62
  63     Note that pointers to any and all classes are already automatically
  64     declared as movable data.
  65
  66     @library{wxbase}
  67     @category{data}
  68
  69     @see wxAnyValueType, wxVariant, @ref overview_cpp_rtti_disabled
  70 */
  71 class wxAny
  72 {
  73 public:
  74     /**
  75         Default constructor. It seeds the object with a null value.
  76     */
  77     wxAny();
  78
  79     /**
  80         Constructs wxAny from data.
  81     */
  82     template<typename T>
  83     wxAny(const T& value);
  84
  85     /**
  86         Constructs wxAny from another wxAny.
  87     */
  88     wxAny(const wxAny& any);
  89
  90     /**
  91         Constructs wxAny, converting value from wxVariant.
  92
  93         @remarks Because of this conversion, it is not usually possible to
  94                  have wxAny that actually holds a wxVariant. If wxVariant
  95                  cannot be converted to a specific data type, wxAny will then
  96                  hold and manage reference to wxVariantData* similar to how
  97                  wxVariant does.
  98     */
  99     wxAny(const wxVariant& variant);
 100
 101     /**
 102         Destructor.
 103     */
 104     ~wxAny();
 105
 106     /**
 107         This template function converts wxAny into given type. In most cases
 108         no type conversion is performed, so if the type is incorrect an
 109         assertion failure will occur.
 110
 111         @remarks For conveniency, conversion is done when T is wxString. This
 112                  is useful when a string literal (which are treated as
 113                  const char* and const wchar_t*) has been assigned to wxAny.
 114
 115                  This template function may not work properly with Visual C++
 116                  6. For full compiler compatibility, please use
 117                  wxANY_AS(any, T) macro instead.
 118     */
 119     template<typename T>
 120     T As() const;
 121
 122     /**
 123         Use this template function for checking if this wxAny holds
 124         a specific C++ data type.
 125
 126         @remarks This template function may not work properly with Visual C++
 127                 6. For full compiler compatibility, please use
 128                 wxANY_CHECK_TYPE(any, T) macro instead.
 129
 130         @see wxAnyValueType::CheckType()
 131     */
 132     template<typename T>
 133     bool CheckType();
 134
 135     /**
 136         Template function that retrieves and converts the value of this
 137         wxAny to the type that T* value is.
 138
 139         @return Returns @true if conversion was successful.
 140     */
 141     template<typename T>
 142     bool GetAs(T* value) const;
 143
 144     /**
 145         Specialization of GetAs() that allows conversion of wxAny into
 146         wxVariant.
 147
 148         @return Returns @true if conversion was successful. Conversion usually
 149                 only fails if variant used custom wxVariantData that did not
 150                 implement the wxAny to wxVariant conversion functions.
 151     */
 152     bool GetAs(wxVariant* value) const;
 153
 154     /**
 155         Returns the value type as wxAnyValueType instance.
 156
 157         @remarks You cannot reliably test whether two wxAnys are of
 158                 same value type by simply comparing return values
 159                 of wxAny::GetType(). Instead use
 160                 wxAnyValueType::CheckType<T>() template function.
 161     */
 162     const wxAnyValueType* GetType() const;
 163
 164     /**
 165         Tests if wxAny is null (that is, whether there is data).
 166     */
 167     bool IsNull() const;
 168
 169     /**
 170         Makes wxAny null (that is, clears it).
 171     */
 172     void MakeNull();
 173
 174     //@{
 175     /**
 176         @name Assignment operators
 177     */
 178     template<typename T>
 179     wxAny& operator=(const T &value);
 180     wxAny& operator=(const wxAny &any);
 181     wxAny& operator=(const wxVariant &variant);
 182     //@}
 183
 184     //@{
 185     /**
 186         @name Equality operators
 187
 188         @remarks Generic template-based comparison operators have not been
 189                 provided for various code consistency reasons, so for custom
 190                 data types you have do something like this:
 191
 192                 @code
 193                 if ( any.CheckType<MyClass*>() &&
 194                      any.As<MyClass*>() == myObjectPtr )
 195                 {
 196                     // Do something if any stores myObjectPtr
 197                 }
 198                 @endcode
 199     */
 200     bool operator==(signed char value) const;
 201     bool operator==(signed short value) const;
 202     bool operator==(signed int value) const;
 203     bool operator==(signed long value) const;
 204     bool operator==(wxLongLong_t value) const;
 205     bool operator==(unsigned char value) const;
 206     bool operator==(unsigned short value) const;
 207     bool operator==(unsigned int value) const;
 208     bool operator==(unsigned long value) const;
 209     bool operator==(wxULongLong_t value) const;
 210     bool operator==(float value) const;
 211     bool operator==(double value) const;
 212     bool operator==(bool value) const;
 213     bool operator==(const char* value) const;
 214     bool operator==(const wchar_t* value) const;
 215     bool operator==(const wxString& value) const;
 216     //@}
 217
 218     //@{
 219     /**
 220         @name Inequality operators
 221     */
 222     bool operator!=(signed char value) const;
 223     bool operator!=(signed short value) const;
 224     bool operator!=(signed int value) const;
 225     bool operator!=(signed long value) const;
 226     bool operator!=(wxLongLong_t value) const;
 227     bool operator!=(unsigned char value) const;
 228     bool operator!=(unsigned short value) const;
 229     bool operator!=(unsigned int value) const;
 230     bool operator!=(unsigned long value) const;
 231     bool operator!=(wxULongLong_t value) const;
 232     bool operator!=(float value) const;
 233     bool operator!=(double value) const;
 234     bool operator!=(bool value) const;
 235     bool operator!=(const char* value) const;
 236     bool operator!=(const wchar_t* value) const;
 237     bool operator!=(const wxString& value) const;
 238     //@}
 239 };
 240
 241 /**
 242     This is value getter macro that is more compatible with older
 243     compilers, such as Visual C++ 6.0.
 244 */
 245 #define wxANY_AS(any, T)
 246
 247
 248 /**
 249     This is type checking macro that is more compatible with older
 250     compilers, such as Visual C++ 6.0.
 251 */
 252 #define wxANY_CHECK_TYPE(any, T)
 253
 254
 255 /**
 256     Size of the wxAny value buffer.
 257 */
 258 enum
 259 {
 260     WX_ANY_VALUE_BUFFER_SIZE = 16
 261 };
 262
 263 /**
 264     Type for buffer within wxAny for holding data.
 265 */
 266 union wxAnyValueBuffer
 267 {
 268     void*   m_ptr;
 269     wxByte  m_buffer[WX_ANY_VALUE_BUFFER_SIZE];
 270 };
 271
 272
 273 /**
 274     @class wxAnyValueType
 275
 276     wxAnyValueType is base class for value type functionality for C++ data
 277     types used with wxAny. Usually the default template will create a
 278     satisfactory wxAnyValueType implementation for a data type, but
 279     sometimes you may need to add some customization. To do this you will need
 280     to add specialized template of wxAnyValueTypeImpl<>. Often your only
 281     need may be to add dynamic type conversion which would be done like
 282     this:
 283
 284     @code
 285         template<>
 286         class wxAnyValueTypeImpl<MyClass> :
 287             public wxAnyValueTypeImplBase<MyClass>
 288         {
 289             WX_DECLARE_ANY_VALUE_TYPE(wxAnyValueTypeImpl<MyClass>)
 290         public:
 291             wxAnyValueTypeImpl() :
 292                 wxAnyValueTypeImplBase<MyClass>() { }
 293             virtual ~wxAnyValueTypeImpl() { }
 294
 295             virtual bool ConvertValue(const wxAnyValueBuffer& src,
 296                                       wxAnyValueType* dstType,
 297                                       wxAnyValueBuffer& dst) const
 298             {
 299                 // GetValue() is a static member function implemented
 300                 // in wxAnyValueTypeImplBase<>.
 301                 MyClass value = GetValue(src);
 302
 303                 // TODO: Convert value from src buffer to destination
 304                 //       type and buffer. If cannot be done, return
 305                 //       false. This is a simple sample.
 306                 if ( dstType->CheckType<wxString>() )
 307                 {
 308                     wxString s = value.ToString();
 309                     wxAnyValueTypeImpl<wxString>::SetValue(s, dst);
 310                 }
 311                 else
 312                 {
 313                     return false;
 314                 }
 315             }
 316         };
 317
 318         //
 319         // Following must be placed somewhere in your source code
 320         WX_IMPLEMENT_ANY_VALUE_TYPE(wxAnyValueTypeImpl<MyClass>)
 321     @endcode
 322
 323     wxAnyValueTypeImplBase<> template, from which we inherit in the above
 324     example, contains the bulk of the default wxAnyValueTypeImpl<> template
 325     implementation, and as such allows you to easily add some minor
 326     customization.
 327
 328     If you need a have complete control over the type interpretation, you
 329     will need to derive a class directly from wxAnyValueType, like this:
 330
 331     @code
 332         template <>
 333         class wxAnyValueTypeImpl<MyClass> : public wxAnyValueType
 334         {
 335             WX_DECLARE_ANY_VALUE_TYPE(wxAnyValueTypeImpl<MyClass>)
 336         public:
 337             virtual void DeleteValue(wxAnyValueBuffer& buf) const
 338             {
 339                 // TODO: Free the data in buffer
 340                 // It is important to clear the buffer like this
 341                 // at the end of DeleteValue().
 342                 buf.m_ptr = NULL;
 343             }
 344
 345             virtual void CopyBuffer(const wxAnyValueBuffer& src,
 346                                     wxAnyValueBuffer& dst) const
 347             {
 348                 // TODO: Copy value from one buffer to another.
 349                 //       dst is already uninitialized and does not
 350                 //       need to be freed.
 351             }
 352
 353             virtual bool ConvertValue(const wxAnyValueBuffer& src,
 354                                       wxAnyValueType* dstType,
 355                                       wxAnyValueBuffer& dst) const
 356             {
 357                 // TODO: Convert value from src buffer to destination
 358                 //       type and buffer.
 359             }
 360
 361             //
 362             // Following static functions must be implemented
 363             //
 364
 365             static void SetValue(const T& value,
 366                                  wxAnyValueBuffer& buf)
 367             {
 368                 // TODO: Store value into buf.
 369             }
 370
 371             static const T& GetValue(const wxAnyValueBuffer& buf)
 372             {
 373                 // TODO: Return reference to value stored in buffer.
 374             }
 375         };
 376
 377         //
 378         // Following must be placed somewhere in your source code
 379         WX_IMPLEMENT_ANY_VALUE_TYPE(wxAnyValueTypeImpl<MyClass>)
 380
 381     @endcode
 382
 383     @library{wxbase}
 384     @category{data}
 385
 386     @see wxAny
 387 */
 388 class wxAnyValueType
 389 {
 390 public:
 391     /**
 392         Default constructor.
 393     */
 394     wxAnyValueType();
 395
 396     /**
 397         Destructor.
 398     */
 399     virtual ~wxAnyValueType();
 400
 401     /**
 402         Use this template function for checking if wxAnyValueType represents
 403         a specific C++ data type.
 404
 405         @remarks This template function does not work on some older compilers
 406                 (such as Visual C++ 6.0). For full compiler compatibility
 407                 please use wxANY_VALUE_TYPE_CHECK_TYPE(valueTypePtr, T) macro
 408                 instead.
 409
 410         @see wxAny::CheckType()
 411     */
 412     template <typename T>
 413     bool CheckType();
 414
 415     /**
 416         Convert value into buffer of different type. Return false if
 417         not possible.
 418     */
 419     virtual bool ConvertValue(const wxAnyValueBuffer& src,
 420                               wxAnyValueType* dstType,
 421                               wxAnyValueBuffer& dst) const = 0;
 422
 423     /**
 424         Implement this for buffer-to-buffer copy.
 425
 426         @param src
 427             This is the source data buffer.
 428
 429         @param dst
 430             This is the destination data buffer that is in either
 431             uninitialized or freed state.
 432     */
 433     virtual void CopyBuffer(const wxAnyValueBuffer& src,
 434                             wxAnyValueBuffer& dst) const = 0;
 435
 436     /**
 437         This function is called every time the data in wxAny
 438         buffer needs to be freed.
 439     */
 440     virtual void DeleteValue(wxAnyValueBuffer& buf) const = 0;
 441
 442     /**
 443         This function is used for internal type matching.
 444     */
 445     virtual bool IsSameType(const wxAnyValueType* otherType) const = 0;
 446 };
 447
 448 /**
 449     This is type checking macro that is more compatible with older
 450     compilers, such as Visual C++ 6.0.
 451 */
 452 #define wxANY_VALUE_TYPE_CHECK_TYPE(valueTypePtr, T)